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  1. #1
    Join Date
    Oct 2009
    Location
    New Haven, CT, USA
    Posts
    629

    Default potential 8.1 HO re-power advise

    My now 30 year old 454's have given me ten great years of service but the boat has always been underpowered (Trojan International, 33', 17k pounds fully loaded). I am looking a pair of 8.1 HO's as a bump up and a compromise between a full diesel re-power which I have taken off the table.

    Right now, I'm cruising at about 16-17k knots and by all accounts a 20-21k cruise should be reasonable with the big jump in torque. Has anyone here done same on a boat of similar size and have feedback? I know I'll probably burn less fuel but keeping my expectations here really low. 10% less would be a homerun which should be reasonable.

    - Is the footprint of the 8.1's very close to the 454's? I have the taller flame arrestor and still have a few additional inches of clearance above that.

    - I have 1.25" shafts now and read that those should be ok if one is aquamet 22. I replaced one a few years ago and it is aquamet , the other is original but just dye tested last year.

    - How do I determine the required transmission setup? The ones I'm looking at have ZF Hurth 630 A1 2.0 which I'm told are down angle units and believe that's what I need for my hull. On my model Trojan, the engines are set back and the shafts are pretty short and at a steep angle.
    I assume the ratio is 2:1 but will verify. My current tran is 1.5:1.

    thanks,
    Bob

  2. #2
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    7,850

    Default Re: potential 8.1 HO re-power advise

    Biggest question I have is where are you gonna get them ??

    The best answer on the gear probably comes from a marine architect......a good prop shop can share lots of experience as can a yard that specializes in repowers. More reduction will let the engine work easier.....

    you can get the install drawing out of the Crusader installation manual, for the 8.1's.....I think I have some install drawings for the inline gear behind a 7.4 but won't have access for a few more hours...will email what I have later...

  3. #3
    Join Date
    Sep 2010
    Location
    Jersey Shore
    Posts
    5,546

    Default Re: potential 8.1 HO re-power advise

    I have a Bertram Built Trojan 10 meter international with new Gen 6 FWC crusaders I will sell you the whole boat for 10K With a Kohler 5E Genset. I own too many boats.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  4. #4
    Join Date
    Oct 2009
    Location
    New Haven, CT, USA
    Posts
    629

    Default Re: potential 8.1 HO re-power advise

    Quote Originally Posted by makomark View Post
    Biggest question I have is where are you gonna get them ??

    The best answer on the gear probably comes from a marine architect......a good prop shop can share lots of experience as can a yard that specializes in repowers. More reduction will let the engine work easier.....

    you can get the install drawing out of the Crusader installation manual, for the 8.1's.....I think I have some install drawings for the inline gear behind a 7.4 but won't have access for a few more hours...will email what I have later...
    Mark,

    Thanks, I called a prop shop who I've used before and they are going to send me something to figure out the props/transmission gearing.
    To answer your first question, I have a lead a pair of used ones. Just doing some preliminary investigating and then might go see them this week.
    Any dimensional drawings would help compare old vs. new. I "think" I have plenty of room but want to be sure.

    Bob

  5. #5
    Join Date
    Oct 2009
    Location
    New Haven, CT, USA
    Posts
    629

    Default Re: potential 8.1 HO re-power advise

    Quote Originally Posted by Docksidemarineservices View Post
    I have a Bertram Built Trojan 10 meter international with new Gen 6 FWC crusaders I will sell you the whole boat for 10K With a Kohler 5E Genset. I own too many boats.

    Chris, that would be great option but I've put way to much time in customizing the one I have. Feel free to send me some pics though, I might know a guy who would be interested.

    Bob

    rdunne14 AT Comcast DOT net

  6. #6
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    7,850

    Default Re: potential 8.1 HO re-power advise

    sent you four drawings...one that should be close enough for your baseline and then the others are the 496 with various gears...

  7. #7
    Join Date
    Sep 2010
    Location
    Jersey Shore
    Posts
    5,546

    Default Re: potential 8.1 HO re-power advise

    Quote Originally Posted by bobct View Post
    Chris, that would be great option but I've put way to much time in customizing the one I have. Feel free to send me some pics though, I might know a guy who would be interested.

    Bob

    rdunne14 AT Comcast DOT net
    Have him Message me Docksidemarineservices at comcast dot net.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

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